IB Physics SL D 3 3 Crossed Electric and Magnetic Fields Questions

Analyse crossed electric and magnetic fields by balancing electric and magnetic forces, selecting velocities and predicting charged-particle paths.

Exam points

Explain and calculate the balance of electric and magnetic forces on charged particles in crossed fields.
Determine field strength, direction and undeflected motion using E=vB and force directions.
Predict how changing particle charge, mass or velocity affects its path in crossed fields.

[Maximum number: 2]

Two oppositely charged parallel plates are a distance 8.0 cm apart. The potential difference between the plates is 120 V . An alpha particle is placed on the positively charged plate and released from rest. Gravity is ignored.

Figure for Question IB Physics SL D 3 3 Crossed Electric and Magnetic Fields Questions question 1 — IB Physics SL

A magnetic field directed into the plane of the page is now established between the plates. An alpha particle enters the region between the plates with a horizontal speed of $5.0 \times 10^{5} \mathrm{~m} \mathrm{~s}^{-1}$ . The particle is not deflected.

Calculate the magnitude of the magnetic field.

$\begin{aligned} F_{\mathrm{m}} =F_{\mathrm{e}} \text { OR } q v B=q E \text { OR } B=F_{\mathrm{e}} / q v \quad B =\ll \frac{E}{v}=\frac{1.5 \times 10^{3}}{5.0 \times 10^{5}}=>3.0 \times 10^{-3} T \end{aligned}$

Award [2] if $3.0 \times 10^{-3}$ « T » is seen as the answer without working.

Allow ECF from a) and b) i)

[2]

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IB Physics SL D 3 3 Crossed Electric and Magnetic Fields Questions question 1